In the presence of ground layers which are not capable of bearing high loads, and in the case of building constructions having to meet stringent requirements in respect to stability and serviceability, use is often made of deep foundations in order to dissipate building-construction loads. This is usually done using pile-like load-bearing members which are incorporated in the lower-level, load-bearing layers of soil and introduce the loads from the building construction there with a low level of deformation.
In loose ground, the load is dissipated from the pile-like load-bearing members to the ground surrounding them by way of the two resistance fractions: lateral friction and point bearing pressure. The sum of the resistance here is dependent on the level of settlement of the pile-like load-bearing members. It is usually assumed that the maximum point resistance is mobilized at a level of settlement at the head of the load-bearing members of s/D=0.1 (where s=level of settlement at the head of the load-bearing member, D=diameter of the load-bearing member). Usually relatively small levels of settlement are necessary for the maximum lateral friction.
When the load-bearing member is incorporated in unyielding ground/solid rock, in contrast to loose ground, only very low levels of settlement, if any at all, are necessary in order to mobilize the resistance. Nevertheless, the load is dissipated (theoretically) exclusively via the point bearing pressure/point resistance, since the lateral friction is not mobilized owing to settlement being absent.
In design practice, this results in predominantly only the point resistance being used in the calculations. This means that, by the absence of lateral friction in load-bearing members which are founded in unyielding ground, loads can be transmitted into the ground merely via the point resistance. Load-bearing reserves from the lateral friction thus cannot be utilized. This results in a greater number of piles being required and/or in larger diameters or longer lengths of the piles. On account of the lateral-friction fraction being absent, load-bearing members founded in this way therefore have, in relative terms, only a low load-bearing capacity.
If, however, a certain amount of settlement can be permitted and ensured, then it is possible to mobilize the lateral friction and therefore to increase the overall resistance. If the strength of the bedrock is high to very high, however, it normally cannot be assumed that there is sufficiently high levels of settlement present to activate the lateral friction.
Accordingly, it is an aim of the present invention to provide design measures and methods which allow for a specific minimum level of settlement of the pile-like load-bearing members and thus always ensure the activation of the lateral friction. The amount of settlement here should be definable and foreseeable.